On Sunday against San Diego, the Seahawks’ noted Legion of Boom secondary looked like an entire group of fairly normal guys, allowing quarterback Philip Rivers to complete 76 percent of his passes for 284 yards and three touchdowns.

Allen had five catches, but it was Rivers and tight end Antonio Gates who connected on those three TD passes against a Seahawks defense that led the NFL in fewest points allowed last season.

“We didn’t execute the way we normally do,” safety Earl Thomas said. “We never (usually) let anybody off the hook with penalties. They kept the ball and kept making great plays.”

Particularly on third down, when Rivers was 9-for-12 with two touchdowns.

Thomas said the Seahawks “showed something new” on defense, “but it didn’t work out the way we thought it would work out. They did a great job. Their quarterback is a great quarterback. We just let them off the hook a couple times and they took advantage of it.”

Thomas, cornerback Byron Maxwell and safety Kam Chancellor all missed some action in the second half, when they cramped in the heat and went into the locker room for intravenous fluids.

Asked if it’s a challenge for a team that practices in mild Northwest weather to play on a day when the temperature on the field was said to reach into triple digits, Maxwell had a theory unrelated to the heat.

“I think it’s more the fact that we’ve got to get off the field on third down,” Maxwell said. “There were a lot of plays we could have limited if we got off the field. I think that was definitely on us.”

The secondary was already without injured backups Tharold Simon and Jeremy Lane, and when the starters had to come out with cramps, newcomers Marcus Burley and Josh Thomas were tossed onto the field.

“They do a good job of bringing in guys with the right mentality,” Maxwell said of the personnel department having targeted Burley and Thomas as players who could fit in. “Marcus made some great plays, and Josh made a great play on a deep ball.”

Gates offered a higher opinion of the Seattle secondary than did Allen.

“They play zone, and the ‘Legion of Boom’ is what I’ve been hearing about all week, so they obviously believe in their skills to cover. It was just a situation where, fortunately, I was matched up on linebackers at times and I was able to come away with the win and Philip was able to put the ball where no other player could get it.”

Chancellor was on Gates for one of his touchdowns.

“He’s definitely crafty and smart,” Chancellor said. “He has a quarterback who looks for him, knows the moves he makes and gets the ball to him.”

Thomas said the troubles in the secondary were not from a lack of effort.

“I think I left everything out there,” Thomas said. “I do not have anything to hold my head down about. If somebody beats us, I always feel like it was luck. It’s not about them. No matter if we win or lose, it’s not going to dictate who we are. We will understand what happened out there today when we watch the film.”

Never miss a local story.

Sign up today for unlimited digital access to our website, apps, the digital newspaper and more.